This application claims the priority benefit of Japanese application serial no. 2001-263636, filed on Aug. 31, 2001, 2002-221837 filed on Jul. 30, 2002.
1. Field of the Invention
This invention relates to a driving device for driving an image forming apparatus such as a copy machine, a printer or a facsimile etc.
2. Description of the Related Art
The driving device used in the driving unit of the image forming apparatus of electrophotography type such as a copy machine, a printer or a facsimile etc., is constructed by assembling a electromagnetic clutch in order to temporarily stop the driving parts or stop the driven parts alone during images formation. For example, the transporting roller, which is used on the transporting passage of the recording material form the sheet feeding device to the resist roller, can be connected to or released from the driving unit by the electromagnetic clutch. And the fixing roller of the fixing device also can be connected to or released from the driving unit by the electromagnetic clutch.
When the electromagnetic clutch is used in the driving device of the fixing device, with regard to continuous passage of the transferring papers, in a way that the drivings of the photoreceptor etc. and the fixing device can be independently controlled so that driving of the fixing device can be stopped for a time period after the previous transferring paper has passed through and until the next transferring paper is received by the fixing device. Then, immediately after the last transferring paper passes the fixing device, the fixing device can be stopped. In this way, the operation time of the fixing device is less than that of the entire image forming apparatus, and therefore the durability and the life of the fixing device can be effective extended.
The general electromagnetic clutch is of a magnetization type. In the magnetization type electromagnetic clutch, the magnetic field is created by the coil inside the clutch under the influence of the applied rated voltage, and the excitation type electromagnetic clutch is connected to the gears. However there are several drawbacks from using the magnetization type electromagnetic clutch in the driving device of the fixing device as described as follows. In the fixing device, usually a paper jam occurs when the transferring paper is clamped by the fixing roller and the pressure roller. In this condition, it is necessary to remove the jammed paper by manually turning the knob set on the driving shaft of the fixing roller. For removing the jammed paper, the front cover of the image forming apparatus is opened, and for the safety of the user, the interlock switch is turned off. In this situation, the rated voltage supply to the magnetization type is cut off and therefore the electromagnetic clutch and the driving will not be connected. Therefore, it is difficult to remove the jammed paper.
On the contrary, the non-magnetization type electromagnetic clutch will operate reversely compared to the magnetization type electromagnetic clutch when it is electrified. Therefore when the non-magnetization type electromagnetic clutch is connected to drive and when it is not electrified, then the jammed paper can be removed.
FIG. 4 is an example showing the non-magnetization type electromagnetic clutch. FIG. 4 is a cross-sectional view taken along an axial direction of the rotational shaft. The coil 27 and the outer yoke 28 are arranged on the fixing side of the non-magnetization type electromagnetic clutch. The driving shaft 29, the rotor 30 and the inner yoke 31 are arranged on the rotational side of the non-magnetization type electromagnetic clutch. The permanent magnet 32 is arranged on an end of the magnetism clearance portion between the outer yoke 28 at the fixing side and the inner yoke 31 at the rotational side.
When the coil 27 is not electrified, the magnetic circuit is formed by the permanent magnet 32 between the permanent magnet 32 and the armature 33. The electromagnetic attraction is generated between the outer yoke 28, the magnetic tip of the inner yoke 31 and the armature 33. The armature 33 will be drawn to the sides of the outer yoke 28 and the inner yoke 31 to transmit driving. On the contrary, when the coil 27 is electrified, a reverse magnetic circuit is formed between the permanent magnet 32 and the armature 33 to eliminate the magnetic attraction of the permanent magnet 32. In this way, the armature 33 is free from attraction and is released by the release spring to break driving.
However, there are drawbacks from using the non-magnetization type electromagnetic clutch in the drive device. For cost saving, the driving shaft 29 of the electromagnetic clutch, the bearing of the driving shaft 29 (not shown in FIG. 4) and the bracket supporting the electromagnetic clutch etc., are made of the magnetic material such as free cutting steel or zinc-treating steel plate etc. In this way, if the members beside the non-magnetization type electromagnetic clutch are tinged with magnetism, the permanent magnet 32 inside the electromagnetic clutch is adversely affected. So that the desired rated torque cannot be achieved.
For solving the problems described above, an object of this invention is to provide a driving device, which can maintain a sufficient rated torque of the non-magnetization type electromagnetic clutch. Furthermore, another object of the invention is to provide a fixing device, comprising the driving device, which can maintain a sufficient rated torque, and can perform a stable driving.
In accordance with the above objects and other objects, the present invention provides a driving device. The driving device, comprises a driving motor; and a driving gear. The driving motor and the driving gear is connected by a non-magnetization type electromagnetic clutch. A driving shaft of the electromagnetic clutch is constructed from a non-magnetic material.
According an aspect of the present invention, with regard to the bearings of the driving shaft of the driving device, at least one of the bearings closest to the electromagnetic clutch is made of non-magnetic material.
According to another aspect of the present invention, in the driving device, a supporter of the electromagnetic clutch is made of non-magnetic material.
According to another aspect of the present invention, in the driving device, the electromagnetic clutch is connected to the driving gear with a gear engageably connected to the electromagnetic clutch. The gear connecting the electromagnetic clutch is made of non-magnetic material.
According to another aspect of the present invention, with regard to members constructing the driving device, any one of the members constructed from a magnetic material is disposed at a location outside the influence of the magnetic field of the electromagnetic clutch.
According to another aspect of the present invention, the location not influenced by the magnetic field of the permanent magnet is the place with 80% or the less magnetic field decay. The place with 100% or the less magnetic field decay is favorable. It is same as follows.
According to another aspect of the present invention, in the driving device, a bearing of the driving shaft that is made of magnetic material is disposed at a location outside the influence of the magnetism of the electromagnetic clutch.
According to another aspect of the present invention, in the driving device, a supporter of the electromagnetic clutch that is made of magnetic material is disposed at a location outside the influence of the magnetic filed of the electromagnetic clutch.
According to another aspect of the present invention, in the driving device, a rear plate for installing the driving device is disposed at a location outside the influence of the magnetic field of the electromagnetic clutch.
Additionally, the present invention provides a fixing device, for fixing a toner image on a transferring paper, comprising the driving device described above.
Furthermore, the present invention provide a fixing device, for fixing a toner image on a transferring paper, comprising a driving device, wherein a driving motor and a driving gear is connected by a non-magnetization type electromagnetic clutch.